Measurement of the time-dependent CP asymmetries in Bs0→ J/ψKS0

Abstract: The first measurement of decay-time-dependent CP asymmetries in the decay Bs0 → J/ψKS0 and an updated measurement of the ratio of branching fractions ℬ(formula presented.)→J/ψ(formula presented.)$$ \mathrm{\mathcal{B}}\left({B}_{\mathrm{s}}^0\to J/\psi{K}_{\mathrm{S}}^0\right)/\mathrm{\mathcal{B}}\left({B}^0\to J/\psi {K}_{\mathrm{S}}^0\right) $$ is measured to be0.0431±0.0017stat±0.0012syst±0.0025fs/fd,$$ 0.0431\pm 0.0017\left(\mathrm{stat}\right)\pm 0.0012\left(\mathrm{syst}\right)\pm 0.0025\left({f}_s/{f}_d\right), $$where the last uncertainty is due to the knowledge of the Bs0 and B0 production fractions.[Figure not available: see fulltext.]